Thank you for your reply. The thing that has me most confused in their tutorial is the part where it says "Connect V- to the positive terminal or lead of the load. This puts the sense resistor in-line with the circuit."
If I have TX and RX pins for two sensors each, where would the lead of the load be? I am using Pins 2 and 3 for the GSM module and pins 8 and 9 for the GPS module.